Evolutionary Impact of Cytoplasmic Sex Ratio Distorters on Host Reproductive Biology

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Many animals house bacteria that live inside their cells; some are harmless but others, termed reproductive parasites, selfishly manipulate the host's reproductive system. This project investigates the extent to which a widespread reproductive parasite named Wolbachia has shaped the reproductive biology of a common tropical butterfly Hypolimnas bolina. In some South Pacific islands, Wolbachia selectively kills male butterflies and consequently male H. bolina are rarer on islands with high levels of Wolbachia infection. The study addresses whether new sexual traits have evolved as a result of Wolbachia infection by comparing butterfly populations on islands with different sex ratios. The work will (i) determine the population history of the butterfly using genetic markers; (ii) characterize butterfly sexual characteristics on different islands; and (iii) test whether Wolbachia infection explains the evolution of sexual characters in H. bolina. Recent evidence indicates that reproductive parasites are widespread in insects and that they can reach extremely high frequencies in natural populations. Given the important impact of infection on the host (male-killing being a dramatic example), reproductive parasites could play a major role in the design of reproductive systems. The Wolbachia-Hypolimnas case study provides a powerful test for this hypothesis.